After a long and protracted process, the remaining contenders vying for Yahoo‘s core business are due to submit their final offers on Monday. Just one last hitch: the winning bidder might be “on the hook for more than $1 billion in immediate payments to Mozilla, the company that makes the Firefox web browser,” The New York Times reports.

Chalk it up to Mayer’s stubborn resolve to reinvigorate Yahoo’s search business. She secured Yahoo’s place as the default search for Firefox in 2014 by agreeing to pay Mozilla $375 million per year—$100 million more than prior search partner Google—as part of a five-year contract. According to the Times, Mayer “personally” added a clause that makes it possible for Mozilla to demand the balance on the contract if Yahoo comes under new ownership.